For a moving body such as an inverted two-wheeled vehicle, it is necessary to estimate a tilt angle with high accuracy in order to maintain an inverted posture. Not only for the two-wheeled type vehicle but also for a walking type moving body or a caterpillar-driven moving body, the estimation of the tilt angle with high accuracy is required.
Conventionally, mechanisms for estimating a tilt angle include a system using a gyro (angular velocity) sensor and a system using an acceleration sensor. In the system using a gyro sensor, a tilt angle is obtained by integrating an output signal of the gyro sensor. However, an offset noise is originally superimposed on the output signal of the gyro sensor, so there is a problem in that a deviation from a true value is gradually increased.
In the system using an acceleration sensor, the tilt angle is calculated using a geometric relation obtained by a two or more axial acceleration sensor. According to the system, the tilt angle is calculated from values of a biaxial gravity acceleration, so there is a problem in that the estimation accuracy is degraded unless the estimation is carried out in a static state. In particular, when the moving body is accelerated/decelerated, a component generated by the acceleration/deceleration is superimposed as noise on the biaxial acceleration sensor.
Further, there is also proposed a system for estimating a tilt angle by an autonomous inertia navigation system (INS) using a gyro sensor and a triaxial acceleration sensor. However, the problem of the offset noise in the gyro sensor and the problem of the noise caused by the acceleration/deceleration of the acceleration sensor as described above are still unsolved.
Note that Patent Document 1 discloses a technique for using a gyro sensor and an accelerometer to be switched for each frequency band. However, the technique is not relevant to the moving body with a tilt angle estimating mechanism.    [Patent Document 1] Japanese Unexamined Patent Application Publication No. 4-346021